The present invention relates to three dimensional optical memory storage, and in particular to the use of polymer nanocomposite materials for three dimensional optical memory storage. Local two-photon-induced photobleaching of particles in an array of particles in the nanocomposite material causes each particle to perform as an individual bit.
In the present invention, local photosensitive changes are effected in particles in the nanocomposite. An example of the local photosensitive change is photobleaching, and the present invention will be particularly described herein with reference to photobleaching.
Further advances in computer technology depend critically on the development of materials for high-density memory storage. Intensive research is focused on designing materials for three-dimensional (3D) optical memory storage, since in 3D the capacity of data storage is a function of 1/xcex3 compared to 1/xcex2 for two-dimensional media, where xcex is the addressing wavelength. To date, such materials are represented by transparent polymer glasses containing molecularly dispersed photochromic species. Optical recording is achieved by inducing local photochemical changes in the chromophore, which lead to two distinct molecular forms with different optical properties.
For instance, U.S. Pat. No. 5,325,324 discloses three-dimensional optical memory, in which selected domains, e.g., 103xc3x97103 domains arrayed in a plane within a three-dimensional volume of active medium, are temporally and spatially simultaneously illuminated by two radiation beams.
U.S. Pat. No. 5,694,249 discloses a three-dimensional optical memory element made of glass. The glass includes a glass matrix with a first refractive index and a plurality of spots distributed in the glass matrix that have a different refractive index. The spots are formed at the focal point of a laser.
U.S. Pat. No. 5,268,862 discloses an active medium, e.g., a photochromic material in a three-dimensional matrix, e.g., a polymer. The active medium is illuminated by two UV laser light beams in selected regions. Two-photon absorption effects a change in the photochromic material that may be made to fluoresce for reading.
U.S. Pat. No. 5,289,407 discloses alteration of the index of refraction of a photopolymer by two-photon excitation. Memories that rely on fluorescence modulation are stated to suffer the limitation that their useful life is limited by photobleaching. U.S. Pat. No. 5,034,613 discloses two-photon laser microscopy.
WO 98/53448 discloses three-dimensional optical memory with fluorescent photosensitive material.
Further improvements in three-dimensional optical memory storage are required.
A new approach to three-dimensional optical memory storage has now been found.
Accordingly, one aspect of the present invention provides a method for providing three dimensional optical memory storage, comprising:
subjecting a nanocomposite to irradiation, said nanocomposite comprising a matrix of particles of a core resin and a shell resin, said shell resin forming a continuous phase of the matrix, said particles of core resin containing at least one photosensitive compound and being in an array in said matrix, said continuous phase being substantially free of said photosensitive compound;
said irradiation being selectively focused on individual particles in said array to effect local photo-sensitive changes in said individual particles, said irradiation being two-photon irradiation of a wavelength to effect said local photo-sensitive changes.
In preferred embodiments of the invention, said local photo-sensitive change is photobleaching.
In embodiments, particles adjacent to the selected particle in the direction of irradiation are photobleached by less than 25%. Preferably, the selected particle is photobleached by more than 50%.
In further embodiments, the core resin comprises a latex of poly(methyl methacrylate), and the shell resin comprises a copolymer of methyl methacrylate and butyl methacrylate monomers.
In other preferred embodiments, the core resin is in a liquid state and is surrounded by a first shell resin to contain the liquid core and a second shell resin that forms the continuous phase of the matrix.
In other embodiments, the particles comprise a latex of an encapsulated polymer of copolymer wherein the core and shell resins are polymers selected from the group consisting of styrene-butadiene, styrene, acrylate, methacrylate, polyesters, and mixtures thereof.
In still further embodiments, the core particles are present in an amount of from about 0.1 to about 70 weight percent based on the total weight of the media, the shell resin is present in amounts of from about 30 to about 99.9 weight percent based on the total weight of the composition, and the core particles are separated from nearest neighboring core particles by the shell resin continuous phase.